System, method, and apparatus for controlling ion energy distribution in plasma processing systems
Systems and methods for plasma processing are disclosed. An exemplary system may include a plasma processing chamber including a source to produce a plasma in the processing chamber and at least two bias electrodes arranged within the plasma processing chamber to control plasma sheaths proximate to the bias electrodes. A chuck is disposed to support a substrate, and a source generator is coupled to the plasma electrode. At least one bias supply is coupled to the at least two bias electrodes, and a controller is included to control the at least one bias supply to control the plasma sheath(s) proximate to the bias electrodes.
1. A method, comprising:
applying a modified periodic voltage function to an electrode of a substrate support of a process chamber to set a wafer voltage for a wafer, wherein the applying the modified periodic voltage function comprises:
(a) delivering a first plurality of voltage pulses that are delivered during a first period wherein each pulse of the first plurality of voltage pulses comprises a first negative voltage step;
(b) delivering a second plurality of voltage pulses that are delivered during a second period wherein each pulse of the second plurality of voltage pulses comprises a second negative voltage step wherein the first negative voltage step is different than the second negative voltage step; and
repeating (a) and (b) a plurality of times to generate an ion energy distribution function that has a plurality of energy peaks in a plasma formed in the process chamber;
wherein each pulse comprises a portion between the negative voltage step and a positive voltage step of a next pulse; and
wherein the portion between the negative voltage step and the positive voltage step of the next pulse is above or below a slope needed to maintain a constant wafer voltage during the portion between the negative voltage step and the positive voltage step of the next pulse.
2. The method of claim 1 , wherein at least two of the plurality of energy peaks have different amplitudes.
3. The method of claim 2 , further comprising:
adjusting a number of the first plurality of voltage pulses relative to a number of the second plurality of voltage pulses to adjust the percentage of ion flux at a first of the plurality of energy peaks relative to ion flux at a second of the plurality of energy peaks.
4. The method of claim 1 , wherein the ion energy distribution function is selected from one of the following: square, concave with two similar-amplitude peaks, concave with two different-amplitude peaks, sloped, and triangular.
5. The method of claim 1 , further comprising adjusting an output of an ion compensation component to control a slope of the portion between the pulses, and thereby control a width of one or more ion energy distribution function peaks.
6. A system, comprising:
a power supply configured to provide a periodic voltage function to an output configured to couple to a substrate support, the periodic voltage function having pulses having a positive voltage step and a negative voltage step and a portion between the pulses; and
a controller in communication with the power supply and having a non-transitory tangible computer readable medium encoded with instructions, and wherein the controller is configured to execute the instructions, the instructions comprising:
accessing a control pattern associated with a resulting ion energy distribution function having a first energy peak and a second energy peak;
controlling switching of the power supply to effectuate the positive and negative voltage steps;
delivering a first plurality of voltage pulses that are delivered during a first period to achieve the first energy peak, wherein each pulse of the first plurality of voltage pulses comprises a first negative voltage step;
delivering a second plurality of voltage pulses that are delivered during a second period to achieve the second energy peak, wherein each pulse of the second plurality of voltage pulses comprises a second negative voltage step wherein the first negative voltage step is different than the second negative voltage step; and
wherein the portion between the negative voltage step and the positive voltage step of the next pulse is above or below a slope needed to maintain a constant wafer voltage during the portion between the negative voltage step and the positive voltage step of the next pulse.
7. The system of claim 6 , further comprising an ion compensation component coupled to an electrical node between the power supply output and the substrate support, the ion compensation component configured to provide a current or voltage to the substrate support, at least between the pulses, that in combination with the periodic voltage function, controls a slope of the portion between the pulses.
8. The system of claim 7 , wherein the ion compensation component is either a voltage source or a current source.
9. The system of claim 6 , wherein the power supply includes two switches coupled between one or more power sources and the output, wherein a momentary closing of a first of the two switches causes the positive voltage step and a subsequent momentary closing of a second of the two switches causes the negative voltage step.